Coal in its virgin state is sometimes treated to improve its usefulness and thermal energy content. The treatment can include drying the coal and subjecting the coal to a pyrolysis process to drive off low boiling point organic compounds and heavier organic compounds. Thermal treatment of coal, including high and medium volatile bituminous, sub-bituminous and lignite, causes the release of certain volatile hydrocarbon compounds having value for further refinement into transportation liquid fuels and other coal derived chemicals. Subsequently, the volatile components can be removed from the sweep gases exiting the pyrolysis process.
Low concentrations of desirable condensable hydrocarbon compounds evolved in the pyrolysis process is problematic. In addition, the liquid versus gas separation (absorption) to remove the low concentration of volatiles is less energy efficient than that which could be achieved with a higher ratio of condensable hydrocarbon compounds to sweep gas. It would be advantageous if coal could be treated in such a manner that would enable the desirable condensable hydrocarbon liquids to be removed from the coal at much higher concentrations. A process for the treatment of coal having a much higher ratio of condensable hydrocarbon compounds to sweep gas is desirable.